Comparison of localhyphen;density and Hartreendash;Fock calculations of molecular polarizabilities and hyperpolarizabilities

摘要

This paper presents a comparison between density functional theory local density approximation (LDA) and Hartreendash;Fock approximation (HFA) calculations of dipole moments, polarizabilities, and first hyperpolarizabilities, using lsquo;lsquo;comparablersquo;rsquo; basis sets, in order to assess the relative quality of the LDA and the HFA for calculating these properties. Specifically, calculations were done using basis sets of roughly double or triple zeta plus polarization quality, with and without added fieldhyphen;induced polarization (FIP) functions, for the seven small molecules H2, N2, CO, CH4, NH3, H2O, and HF, using the HFA option in the program HONDO8 and the LDA options in the programs DMol and deMon. For the calculationswithoutFIP functions, the results from HONDO8 HFA and deMon LDA, both of which use Gaussian basis sets, are very similar, while DMol, which uses a LDA numerical atomic orbital basis set, gives substantially better results. Adding FIP functions does much to alleviate these observed basis set artifacts and improves agreement with experiment.WithFIP functions, the results from the two sets of LDA calculations (deMon and DMol) are very similar to each other, but differ markedly from the HFA results, and the LDA results are in significantly better agreement with experiment. This is particularly true for the hyperpolarizabilities. This appears to be the first detailed study of DFT calculations of molecular first hyperpolarizabilities. We note that closer attention to numerical details of the finite field calculation of bgr;ddarr; is necessary than would usually be the case with traditionalabinitiomethods. A proof that the Hellmannndash;Feynman theorem holds for Kohnndash;Sham calculations is included in the Appendix.